Selective capping processes and structures formed thereby

ABSTRACT

Embodiments disclosed herein relate generally to capping processes and structures formed thereby. In an embodiment, a conductive feature, formed in a dielectric layer, has a metallic surface, and the dielectric layer has a dielectric surface. The dielectric surface is modified to be hydrophobic by performing a surface modification treatment. After modifying the dielectric surface, a capping layer is formed on the metallic surface by performing a selective deposition process. In another embodiment, a surface of a gate structure is exposed through a dielectric layer. A capping layer is formed on the surface of the gate structure by performing a selective deposition process.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a divisional of U.S. patent application Ser. No.15/880,389, filed on Jan. 25, 2018, entitled “Selective CappingProcesses and Structures Formed Thereby,” which application claims thebenefit of and priority to U.S. Provisional Patent Application No.62/591,598, filed on Nov. 28, 2017, entitled “Selective CappingProcesses and Structures Formed Thereby,” which are incorporated hereinby reference in their entirety.

BACKGROUND

As the semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs, challenges from both fabrication and design issues haveresulted in the development of three-dimensional designs, such as a FinField Effect Transistor (FinFET). FinFET devices typically includesemiconductor fins with high aspect ratios and in which channel andsource/drain regions are formed. A gate is formed over and along thesides of the fin structure (e.g., wrapping) utilizing the advantage ofthe increased surface area of the channel to produce faster, morereliable, and better-controlled semiconductor transistor devices.However, with the decreasing in scaling, new challenges are presented.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a three-dimensional view of example simplified Fin FieldEffect Transistors (FinFETs) in accordance with some embodiments.

FIGS. 2A-B, 3A-B, 4A-B, 5A-B, 6A-B, 7A-B, 8A-B, 9A-B, 10A-B, 11A-B,12A-B, 13A-B, 14A-B, and 15A-B are cross-sectional views of respectiveintermediate structures at intermediate stages in an example process offorming a semiconductor device in accordance with some embodiments.

FIGS. 16A-B, 17A-B, 18A-B, and 19A-B are cross-sectional views ofrespective intermediate structures at intermediate stages in anotherexample process of forming a semiconductor device in accordance withsome embodiments.

FIG. 20 is a flow chart of an example process of forming a semiconductordevice in accordance with some embodiments.

FIGS. 21 through 28 are cross-sectional views of respective intermediatestructures at intermediate stages in an example process of forming asemiconductor device in accordance with some embodiments.

FIG. 29 is a flow chart of an example process of forming a semiconductordevice in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

Embodiments disclosed herein relate generally to forming a capping layer(e.g., metal cap) on a metallic surface and to structures formedthereby. In some embodiments, a dielectric surface of a dielectric layercan be modified before a selective deposition for forming a cappinglayer is performed. In such embodiments, the modified surface may serveas a protective layer for the dielectric layer to, for example, improveselectivity of the selective deposition and reduce damage to thedielectric layer. In some embodiments, a selective deposition forforming a capping layer on a gate structure is performed. The cappinglayer on the gate structure can reduce a resistance of a contact to thegate structure, and more particularly, for a gate structure on a shortchannel device. Other advantages of some embodiments may be achieved.

The foregoing broadly outlines some aspects of embodiments describedherein. Some embodiments described herein are described in the contextof Fin Field Effect Transistors (FinFETs), and more particularly, in thecontext of a replacement gate process for FinFETs. Some embodimentsdescribed herein are described in the context of conductive features ina metallization. Implementations of some aspects of the presentdisclosure may be used in other processes and/or in other devices. Forexample, other example devices can include planar FETs, Horizontal GateAll Around (HGAA) FETs, Vertical Gate All Around (VGAA) FETs, nanowirechannel FETs, and other devices. Other example processes can include agate-first process. Some variations of the example methods andstructures are described. A person having ordinary skill in the art willreadily understand other modifications that may be made that arecontemplated within the scope of other embodiments. Although methodembodiments may be described in a particular order, various other methodembodiments may be performed in any logical order and may include feweror more steps than what is described herein.

FIG. 1 illustrates an example of simplified FinFETs 40 in athree-dimensional view. Other aspects not illustrated in or describedwith respect to FIG. 1 may become apparent from the following figuresand description. The structure in FIG. 1 may be electrically connectedor coupled in a manner to operate as, for example, one transistor ormore, such as four transistors.

The FinFETs 40 comprise fins 46 a and 46 b on a semiconductor substrate42. The semiconductor substrate 42 includes isolation regions 44, andthe fins 46 a and 46 b each protrude above and from between neighboringisolation regions 44. Gate dielectric layers 48 a and 48 b are alongsidewalls and over top surfaces of the fins 46 a and 46 b, and gateelectrodes 50 a and 50 b are over the gate dielectric layers 48 a and 48b, respectively. Further, masks 52 a and 52 b are over the gateelectrodes 50 a and 50 b, respectively. Source/drain regions 54 a-f aredisposed in respective regions of the fins 46 a and 46 b. Source/drainregions 54 a and 54 b are disposed in opposing regions of the fin 46 awith respect to the gate dielectric layer 48 a and gate electrode 50 a.Source/drain regions 54 b and 54 c are disposed in opposing regions ofthe fin 46 a with respect to the gate dielectric layer 48 b and gateelectrode 50 b. Source/drain regions 54 d and 54 e are disposed inopposing regions of the fin 46 b with respect to the gate dielectriclayer 48 a and gate electrode 50 a. Source/drain regions 54 e and 54 fare disposed in opposing regions of the fin 46 b with respect to thegate dielectric layer 48 b and gate electrode 50 b.

In some examples, four transistors may be implemented by including: (1)source/drain regions 54 a and 54 b, gate dielectric layer 48 a, and gateelectrode 50 a; (2) source/drain regions 54 b and 54 c, gate dielectriclayer 48 b, and gate electrode 50 b; (3) source/drain regions 54 d and54 e, gate dielectric layer 48 a, and gate electrode 50 a; and (4)source/drain regions 54 e and 54 f, gate dielectric layer 48 b, and gateelectrode 50 b. As indicated, some source/drain regions may be sharedbetween various transistors, and other source/drain regions that are notillustrated as being shared may be shared with neighboring transistorsthat are not illustrated, for example. In some examples, various ones ofthe source/drain regions may be connected or coupled together such thatFinFETs are implemented as two functional transistors. For example, ifneighboring (e.g., as opposed to opposing) source/drain regions 54 a-fare electrically connected, such as through coalescing the regions byepitaxial growth (e.g., source/drain regions 54 a and 54 d beingcoalesced, source/drain regions 54 b and 54 e being coalesced, etc.),two functional transistors may be implemented. Other configurations inother examples may implement other numbers of functional transistors.

FIG. 1 further illustrates reference cross-sections that are used inlater figures. Cross-section A-A is in a plane along, e.g., channels inthe fin 46 a between opposing source/drain regions 54 a-c. Cross-sectionB-B is in a plane perpendicular to cross-section A-A and is acrosssource/drain region 54 a in fin 46 a and across source/drain region 54 din fin 46 b. Subsequent figures refer to these reference cross-sectionsfor clarity. The following figures ending with an “A” designationillustrate cross-sectional views at various instances of processingcorresponding to cross-section A-A, and the following figures endingwith a “B” designation illustrate cross-sectional views at variousinstances of processing corresponding to cross-section B-B. In somefigures, some reference numbers of components or features illustratedtherein may be omitted to avoid obscuring other components or features;this is for ease of depicting the figures.

FIGS. 2A-B through 15A-B are cross-sectional views of respectiveintermediate structures at intermediate stages in an example process offorming a semiconductor device in accordance with some embodiments.FIGS. 2A and 2B illustrate a semiconductor substrate 70. Thesemiconductor substrate 70 may be or include a bulk semiconductorsubstrate, a semiconductor-on-insulator (SOI) substrate, or the like,which may be doped (e.g., with a p-type or an n-type dopant) or undoped.Generally, an SOI substrate comprises a layer of a semiconductormaterial formed on an insulator layer. The insulator layer may be, forexample, a buried oxide (BOX) layer, a silicon oxide layer, or the like.The insulator layer is provided on a substrate, typically a silicon orglass substrate. Other substrates, such as a multi-layered or gradientsubstrate may also be used. In some embodiments, the semiconductormaterial of the semiconductor substrate may include an elementalsemiconductor including silicon (Si) or germanium (Ge); a compoundsemiconductor including silicon carbide, gallium arsenic, galliumphosphide, indium phosphide, indium arsenide, or indium antimonide; analloy semiconductor including SiGe, GaAsP, AlInAs, AlGaAs, GalnAs,GaInP, or GaInAsP; or a combination thereof.

FIGS. 3A and 3B illustrate the formation of fins 74 in the semiconductorsubstrate 70. In some examples, a mask 72 (e.g., a hard mask) is used informing the fins 74. For example, one or more mask layers are depositedover the semiconductor substrate 70, and the one or more mask layers arethen patterned into the mask 72. In some examples, the one or more masklayers may include or be silicon nitride, silicon oxynitride, siliconcarbide, silicon carbon nitride, the like, or a combination thereof, andmay be deposited by chemical vapor deposition (CVD), physical vapordeposition (PVD), atomic layer deposition (ALD), or another depositiontechnique. The one or more mask layers may be patterned usingphotolithography. For example, a photo resist can be formed on the oneor more mask layers, such as by using spin-on coating, and patterned byexposing the photo resist to light using an appropriate photomask.Exposed or unexposed portions of the photo resist may then be removeddepending on whether a positive or negative resist is used. The patternof the photo resist may then be transferred to the one or more masklayers, such as by using a suitable etch process, which forms the mask72. The etch process may include a reactive ion etch (RIE), neutral beametch (NBE), inductive coupled plasma (ICP) etch, the like, or acombination thereof. The etch process may be anisotropic. Subsequently,the photo resist is removed in an ashing or wet strip processes, forexample.

Using the mask 72, the semiconductor substrate 70 may be etched suchthat trenches 76 are formed between neighboring pairs of fins 74 andsuch that the fins 74 protrude from the semiconductor substrate 70. Theetch process may include a RIE, NBE, ICP etch, the like, or acombination thereof. The etch process may be anisotropic.

FIGS. 4A and 4B illustrate the formation of isolation regions 78, eachin a corresponding trench 76. The isolation regions 78 may include or bean insulating material such as an oxide (such as silicon oxide), anitride, the like, or a combination thereof, and the insulating materialmay be formed by a high density plasma CVD (HDP-CVD), a flowable CVD(FCVD) (e.g., a CVD-based material deposition in a remote plasma systemand post curing to make it convert to another material, such as anoxide), the like, or a combination thereof. Other insulating materialsformed by any acceptable process may be used. In the illustratedembodiment, the isolation regions 78 include silicon oxide that isformed by a FCVD process. A planarization process, such as a chemicalmechanical polish (CMP), may remove any excess insulating material andany remaining mask (e.g., used to etch the trenches 76 and form the fins74) to form top surfaces of the insulating material and top surfaces ofthe fins 74 to be coplanar. The insulating material may then be recessedto form the isolation regions 78. The insulating material is recessedsuch that the fins 74 protrude from between neighboring isolationregions 78, which may, at least in part, thereby delineate the fins 74as active areas on the semiconductor substrate 70. The insulatingmaterial may be recessed using an acceptable etch process, such as onethat is selective to the material of the insulating material. Forexample, a chemical oxide removal using a CERTAS® etch or an AppliedMaterials SICONI tool or dilute hydrofluoric (dHF) acid may be used.Further, top surfaces of the isolation regions 78 may have a flatsurface as illustrated, a convex surface, a concave surface (such asdishing), or a combination thereof, which may result from an etchprocess.

A person having ordinary skill in the art will readily understand thatthe processes described with respect to FIGS. 2A-B through 4A-B are justexamples of how fins 74 may be formed. In other embodiments, adielectric layer can be formed over a top surface of the semiconductorsubstrate 70; trenches can be etched through the dielectric layer;homoepitaxial structures can be epitaxially grown in the trenches; andthe dielectric layer can be recessed such that the homoepitaxialstructures protrude from the dielectric layer to form fins. In stillother embodiments, heteroepitaxial structures can be used for the fins.For example, the fins 74 can be recessed (e.g., after planarizing theinsulating material of the isolation regions 78 and before recessing theinsulating material), and a material different from the fins may beepitaxially grown in their place. In an even further embodiment, adielectric layer can be formed over a top surface of the semiconductorsubstrate 70; trenches can be etched through the dielectric layer;heteroepitaxial structures can be epitaxially grown in the trenchesusing a material different from the semiconductor substrate 70; and thedielectric layer can be recessed such that the heteroepitaxialstructures protrude from the dielectric layer to form fins. In someembodiments where homoepitaxial or heteroepitaxial structures areepitaxially grown, the grown materials may be in situ doped duringgrowth, which may obviate prior implanting of the fins although in situand implantation doping may be used together. Still further, it may beadvantageous to epitaxially grow a material for an n-type devicedifferent from the material for a p-type device.

FIGS. 5A and 5B illustrate the formation of dummy gate stacks, or moregenerally, dummy gate structures, on the fins 74. The dummy gate stacksare over and extend laterally perpendicularly to the fins 74. Each dummygate stack comprises an interfacial dielectric 80, a dummy gate 82, anda mask 84. The interfacial dielectrics 80, dummy gates 82, and masks 84for the dummy gate stacks may be formed by sequentially formingrespective layers, and then patterning those layers into the dummy gatestacks. For example, a layer for the interfacial dielectrics 80 mayinclude or be silicon oxide, silicon nitride, the like, or multilayersthereof, and may be thermally and/or chemically grown on the fins 74, orconformally deposited, such as by plasma-enhanced CVD (PECVD), ALD, oranother deposition technique. A layer for the dummy gates 82 may includeor be silicon (e.g., polysilicon) or another material deposited by CVD,PVD, or another deposition technique. A layer for the masks 84 mayinclude or be silicon nitride, silicon oxynitride, silicon carbonnitride, the like, or a combination thereof, deposited by CVD, PVD, ALD,or another deposition technique. The layers for the masks 84, dummygates 82, and interfacial dielectrics 80 may then be patterned, forexample, using photolithography and one or more etch processes, likedescribed above, to form the mask 84, dummy gate 82, and interfacialdielectric 80 for each dummy gate stack.

In some embodiments, after forming the dummy gate stacks, lightly dopeddrain (LDD) regions (not specifically illustrated) may be formed in theactive areas. For example, dopants may be implanted into the activeareas using the dummy gate stacks as masks. Example dopants for the LDDregions can include or be, for example, boron for a p-type device andphosphorus or arsenic for an n-type device, although other dopants maybe used. The LDD regions may have a dopant concentration in a range fromabout 10¹⁵ cm⁻³ to about 10¹⁷ cm⁻³.

FIGS. 6A and 6B illustrate the formation of gate spacers 86. Gatespacers 86 are formed along sidewalls of the dummy gate stacks (e.g.,sidewalls of the interfacial dielectrics 80, dummy gates 82, and masks84) and over the fins 74. Residual gate spacers 86 may also be formedalong sidewalls of the fins 74 (not illustrated in FIG. 6B), forexample, depending on the height of the fins 74 above the isolationregions 78. The gate spacers 86 may be formed by conformally depositingone or more layers for the gate spacers 86 and anisotropically etchingthe one or more layers, for example. The one or more layers for the gatespacers 86 may include or be silicon oxygen carbide, silicon nitride,silicon oxynitride, silicon carbon nitride, the like, multi-layersthereof, or a combination thereof, and may be deposited by CVD, ALD, oranother deposition technique. The etch process can include a RIE, NBE,or another etch process.

FIGS. 7A and 7B illustrate the formation of recesses 90 for source/drainregions. As illustrated, the recesses 90 are formed in the fins 74 onopposing sides of the dummy gate stacks. The recessing can be by an etchprocess. The etch process can be isotropic or anisotropic, or further,may be selective with respect to one or more crystalline planes of thesemiconductor substrate 70. Hence, the recesses 90 can have variouscross-sectional profiles based on the etch process implemented. The etchprocess may be a dry etch, such as a RIE, NBE, or the like, or a wetetch, such as using tetramethyalammonium hydroxide (TMAH), ammoniumhydroxide (NH₄OH), or another etchant.

FIGS. 8A and 8B illustrate the formation of epitaxy source/drain regions92 in the recesses 90. The epitaxy source/drain regions 92 may includeor be silicon germanium (Si_(x)Ge_(1-x), where x can be betweenapproximately 0 and 100), silicon carbide, silicon phosphorus, siliconcarbon phosphorus, pure or substantially pure germanium, a III-Vcompound semiconductor, a II-VI compound semiconductor, or the like. Forexample, materials for forming a III-V compound semiconductor includeInAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, andthe like. The epitaxy source/drain regions 92 may be formed in therecesses 90 by epitaxially growing a material in the recesses 90, suchas by metal-organic CVD (MOCVD), molecular beam epitaxy (MBE), liquidphase epitaxy (LPE), vapor phase epitaxy (VPE), selective epitaxialgrowth (SEG), the like, or a combination thereof. As illustrated inFIGS. 8A and 8B, due to blocking by the isolation regions 78, epitaxysource/drain regions 92 are first grown vertically in recesses 90,during which time the epitaxy source/drain regions 92 do not growhorizontally. After the recesses 90 between the isolation regions 78 arefully filled, the epitaxy source/drain regions 92 may grow bothvertically and horizontally to form facets, which may correspond tocrystalline planes of the semiconductor substrate 70. In some examples,different materials are used for epitaxy source/drain regions for p-typedevices and n-type devices. Appropriate masking during the recessing orepitaxial growth may permit different materials to be used in differentdevices.

A person having ordinary skill in the art will also readily understandthat the recessing and epitaxial growth of FIGS. 7A-B and 8A-B may beomitted, and that source/drain regions may be formed by implantingdopants into the fins 74 using the dummy gate stacks and gate spacers 86as masks. In some examples where epitaxy source/drain regions 92 areimplemented, the epitaxy source/drain regions 92 may also be doped, suchas by in situ doping during epitaxial growth and/or by implantingdopants into the epitaxy source/drain regions 92 after epitaxial growth.Example dopants for the source/drain regions can include or be, forexample, boron for a p-type device and phosphorus or arsenic for ann-type device, although other dopants may be used. The epitaxysource/drain regions 92 (or other source/drain region) may have a dopantconcentration in a range from about 10¹⁹ cm⁻³ to about 10²¹ cm⁻³. Hence,a source/drain region may be delineated by doping (e.g., by implantationand/or in situ during epitaxial growth, if appropriate) and/or byepitaxial growth, if appropriate, which may further delineate the activearea in which the source/drain region is delineated.

FIGS. 9A and 9B illustrate the formation of a contact etch stop layer(CESL) 96 and a first interlayer dielectric (ILD) 100 over the CESL 96.Generally, an etch stop layer can provide a mechanism to stop an etchprocess when forming, e.g., contacts or vias. An etch stop layer may beformed of a dielectric material having a different etch selectivity fromadjacent layers or components. The CESL 96 is conformally deposited onsurfaces of the epitaxy source/drain regions 92, sidewalls and topsurfaces of the gate spacers 86, top surfaces of the mask 84, and topsurfaces of the isolation regions 78. The CESL 96 may comprise or besilicon nitride, silicon carbon nitride, silicon carbon oxide, carbonnitride, the like, or a combination thereof, and may be deposited byCVD, PECVD, ALD, or another deposition technique. The first ILD 100 maycomprise or be silicon dioxide, a low-k dielectric material (e.g., amaterial having a dielectric constant lower than silicon dioxide), suchas silicon oxynitride, phosphosilicate glass (PSG), borosilicate glass(BSG), borophosphosilicate glass (BPSG), undoped silicate glass (USG),fluorinated silicate glass (FSG), organosilicate glasses (OSG),SiO_(x)C_(y), Spin-On-Glass, Spin-On-Polymers, silicon carbon material,a compound thereof, a composite thereof, the like, or a combinationthereof. The first ILD 100 may be deposited by spin-on, CVD, FCVD,PECVD, PVD, or another deposition technique.

FIGS. 10A and 10B illustrate the replacement of dummy gate stacks withreplacement gate structures. The first ILD 100 and CESL 96 are formedwith top surfaces coplanar with top surfaces of the dummy gates 82. Aplanarization process, such as a CMP, may be performed to level the topsurface of the first ILD 100 and CESL 96 with the top surfaces of thedummy gates 82. The CMP may also remove the masks 84 (and, in someinstances, upper portions of the gate spacers 86) on the dummy gates 82.Accordingly, top surfaces of the dummy gates 82 are exposed through thefirst ILD 100 and the CESL 96.

With the dummy gates 82 exposed through the first ILD 100 and the CESL96, the dummy gates 82 are removed, such as by one or more etchprocesses. The dummy gates 82 may be removed by an etch processselective to the dummy gates 82, wherein the interfacial dielectrics 80act as etch stop layers, and subsequently, the interfacial dielectrics80 can optionally be removed by a different etch process selective tothe interfacial dielectrics 80. The etch processes can be, for example,a RIE, NBE, a wet etch, or another etch process. Recesses are formedbetween gate spacers 86 where the dummy gate stacks are removed, andchannel regions of the fins 74 are exposed through the recesses.

The replacement gate structures are formed in the recesses formed wherethe dummy gate stacks were removed. The replacement gate structures eachinclude, as illustrated, an interfacial dielectric 110, a gatedielectric layer 112, one or more optional conformal layers 114, and agate electrode 116. The interfacial dielectric 110 is formed onsidewalls and top surfaces of the fins 74 along the channel regions. Theinterfacial dielectric 110 can be, for example, the interfacialdielectric 80 if not removed, an oxide (e.g., silicon oxide) formed bythermal or chemical oxidation of the fin 74, and/or an oxide (e.g.,silicon oxide), nitride (e.g., silicon nitride), and/or anotherdielectric layer formed by CVD, ALD, molecular beam deposition (MBD), oranother deposition technique.

The gate dielectric layer 112 can be conformally deposited in therecesses where dummy gate stacks were removed (e.g., on top surfaces ofthe isolation regions 78, on the interfacial dielectric 110, andsidewalls of the gate spacers 86) and on the top surfaces of the firstILD 100, the CESL 96, and gate spacers 86. The gate dielectric layer 112can be or include silicon oxide, silicon nitride, a high-k dielectricmaterial, multilayers thereof, or other dielectric material. A high-kdielectric material may have a k value greater than about 7.0, and mayinclude a metal oxide of or a metal silicate of hafnium (Hf), aluminum(Al), zirconium (Zr), lanthanum (La), magnesium (Mg), barium (Ba),titanium (Ti), lead (Pb), multilayers thereof, or a combination thereof.The gate dielectric layer 112 can be deposited by ALD, PECVD, MBD, oranother deposition technique.

Then, the one or more optional conformal layers 114 can be conformally(and sequentially, if more than one) deposited on the gate dielectriclayer 112. The one or more optional conformal layers 114 can include oneor more barrier and/or capping layers and one or more work-functiontuning layers. The one or more barrier and/or capping layers can includea nitride, silicon nitride, carbon nitride, and/or aluminum nitride oftantalum and/or titanium; a nitride, carbon nitride, and/or carbide oftungsten; the like; or a combination thereof; and may be deposited byALD, PECVD, MBD, or another deposition technique. The one or morework-function tuning layer may include or be a nitride, silicon nitride,carbon nitride, aluminum nitride, aluminum oxide, and/or aluminumcarbide of titanium and/or tantalum; a nitride, carbon nitride, and/orcarbide of tungsten; cobalt; platinum; the like; or a combinationthereof; and may be deposited by ALD, PECVD, MBD, or another depositiontechnique. In some examples, a capping layer (e.g., a TiN layer) isformed conformally on the gate dielectric layer 112; a barrier layer(e.g., a TaN layer) is formed conformally on the capping layer; and oneor more work-function tuning layers are sequentially formed conformallyon the barrier layer.

A layer for the gate electrodes 116 is formed over the one or moreoptional conformal layers 114 (e.g., over the one or more work-functiontuning layers), if implemented, and/or the gate dielectric layer 112.The layer for the gate electrodes 116 can fill remaining portions ofrecesses where the dummy gate stacks were removed. The layer for thegate electrodes 116 may be or comprise a metal such as tungsten, cobalt,aluminum, ruthenium, copper, multi-layers thereof, a combinationthereof, or the like. The layer for the gate electrodes 116 can bedeposited by ALD, PECVD, MBD, PVD, or another deposition technique.Portions of the layer for the gate electrodes 116, one or more optionalconformal layers 114, and gate dielectric layer 112 above the topsurfaces of the first ILD 100, the CESL 96, and gate spacers 86 areremoved. For example, a planarization process, like a CMP, may removethe portions of the layer for the gate electrodes 116, one or moreoptional conformal layers 114, and gate dielectric layer 112 above thetop surfaces of the first ILD 100, the CESL 96, and gate spacers 86.Each replacement gate structure comprising the gate electrode 116, oneor more optional conformal layers 114, gate dielectric layer 112, andinterfacial dielectric 110 may therefore be formed as illustrated inFIG. 10A.

FIGS. 11A and 11B illustrate the modification of exposed dielectricsurfaces to have modified surfaces 120. As illustrated, the top surfacesof the first ILD 100, CESL 96, gate spacers 86, and gate dielectriclayers 112, which are exposed, are modified to have the modifiedsurfaces 120. The modification of exposed dielectric surfaces can beomitted in some examples.

Generally, in semiconductor processing, dielectric surfaces, unlesstreated to have different properties, are terminated with hydroxylgroups (OH), such as silicon bonded with a hydroxyl group (Si—OH). Si—OHis generally hydrophilic. In some examples, such a hydrophilic surfaceis modified to be hydrophobic.

In some examples, the modification includes exposing the dielectricsurfaces to a reactant/adsorbate chemical to modify the dielectricsurfaces to be hydrophobic. The reactant/adsorbate chemical can reactwith and/or can be adsorbed onto the dielectric surfaces to modify thedielectric surfaces. In some examples, the reactant/adsorbate chemicalcan selectively react with and/or be adsorbed onto the dielectricsurfaces while not substantially reacting with or being adsorbed ontometallic surfaces. Metallic surfaces may, in some instances, not reactwith or adsorb the reactant/adsorbate chemical, while in otherinstances, may adsorb some of the reactant/adsorbate chemical, which canbe desorbed easily. A bonding energy between the reactant/adsorbatechemical and the dielectric surfaces can be relatively small, while abonding energy between the reactant/adsorbate chemical and the metallicsurfaces can be relatively large. Hence, the reactant/adsorbate chemicalmay react and bond with the dielectric surfaces while not significantlyreacting with and/or being adsorbed by the metallic surfaces. Forexample, the reactant/adsorbate chemical can selectively react with thedielectric surfaces of the first ILD 100, CESL 96, gate spacers 86, andgate dielectric layer 112, while not substantially reacting with orbeing adsorbed by the metallic surfaces of the one or more optionalconformal layers 114 and gate electrodes 116.

For example, surfaces of conductive TiN, TaN, AlTiC, AlTiO, AlTiN,and/or the like, which may be implemented as the one or more optionalconformal layers 114 in the replacement gate structure, are examples ofmetallic surfaces, and surfaces of insulating HfO₂, which may beimplemented as the gate dielectric layer 112, are not metallic surfaces.

The reactant/adsorbate chemical includes a hydrophobic functional groupand a mechanism for easily reacting with a dielectric surface that doesnot generally react with a metallic surface or, if capable of beingadsorbed onto a metallic surface, can be easily desorbed from themetallic surface. For example, the hydrophobic functional group caninclude a hydrocarbon chain (e.g., —C_(X)H_(2X+1)), such as —CH₃, —C₂H₅,etc., and the mechanism for easily reacting with a dielectric surfacecan include silicon (Si). Some example reactant/adsorbate chemicals canbe of the general form R—Si(CH₃)₃. More specific examplereactant/adsorbate chemicals include tetramethylsilane (Si(CH₃)₄),N,N-Dimethyltrimethylsilylamine ((CH₃)₂—N—Si—(CH₃)₃), and/or anothersilane derivative with one or more hydrophobic functional groups.

The dielectric surfaces can be exposed to the reactant/adsorbatechemical using various processes. The exposure can be a dry (e.g., gasand/or plasma) process or a wet process. In an example wet process, thesemiconductor substrate 70 on which the dielectric surfaces are formedis immersed into a bath comprising the chemical reactant at atemperature in a range from 20° C. (e.g., room temperature) to 400° C.,and more particularly, from about 20° C. to about 80° C., for a durationin a range from about 5 seconds to about 600 seconds. The bath canfurther be a mixture comprising the chemical reactant and, for example,deionized water (DIW), isopropyl alcohol (IPA), the like, or acombination thereof. For example, a mixture can be R—Si(CH₃)₃, IPA, andDIW at a ratio in a range of (50% to 100% by parts):(0% to 70% byparts):(0% to 70% by parts) (R—Si(CH₃)₃:IPA:DIW).

An example dry process can be implemented by a CVD, ALD, or anotherprocess. The dry process can implement a plasma or may not implement aplasma. In an example CVD process without a plasma, thereactant/adsorbate chemical may be gaseous and mixed with an inertcarrier gas, such as argon, hydrogen, or another carrier gas. A flowrate of the reactant/adsorbate chemical gas can be in a range from about10 sccm to about 1,000 sccm, and a flow rate of the inert carrier gascan be in a range from about 10 sccm to about 3,000 sccm. A ratio of theflow rate of the reactant/adsorbate chemical gas to the flow rate of theinert carrier gas can be in a range from about 0.90:0.10 to about0.05:0.95. A pressure of the example CVD process can be in a range fromabout 0.1 Torr to about 40 Torr. A temperature of the example CVDprocess can be in a range from 20° C. (e.g., room temperature) to 400°C., and more particularly, from about 50° C. to about 300° C. A durationof the example CVD process can be in a range from about 5 seconds toabout 300 seconds.

In a plasma process, the plasma can be a direct plasma or a remoteplasma. In an example CVD process with a direct plasma (e.g., PECVD),the reactant/adsorbate chemical may be gaseous and mixed with an inertcarrier gas, such as argon, hydrogen, helium, or another carrier gas. Aflow rate of the reactant/adsorbate chemical gas can be in a range fromabout 10 sccm to about 1,000 sccm, and a flow rate of the inert carriergas can be in a range from about 10 sccm to about 3,000 sccm. A ratio ofthe flow rate of the reactant/adsorbate chemical gas to the flow rate ofthe inert carrier gas can be in a range from about 0.90:0.10 to about0.05:0.95. A pressure of the example CVD process with a direct plasmacan be in a range from about 0.1 Torr to about 40 Torr. The directplasma of the CVD process may be a capacitively coupled plasma (CCP).The plasma generator of the CVD process with a direct plasma can beoperated with a power in a range from about 10 W to about 1,000 W andwith a frequency in a range from about 13.56 MHz to about 40 MHz. Thesubstrate holder of the CVD process may be unbiased. A temperature ofthe example CVD process with a direct plasma can be in a range from 20°C. (e.g., room temperature) to 400° C., and more particularly, fromabout 50° C. to about 300° C. A duration of the example CVD process witha direct plasma can be in a range from about 5 seconds to about 300seconds.

In an example CVD process with a remote plasma (e.g., remote plasmaenhanced CVD (RPECVD)), the reactant/adsorbate chemical may be gaseousand mixed with an inert carrier gas, such as argon, hydrogen, helium, oranother carrier gas. A flow rate of the reactant/adsorbate chemical gascan be in a range from about 10 sccm to about 1,000 sccm, and a flowrate of the inert carrier gas can be in a range from about 10 sccm toabout 3,000 sccm. A ratio of the flow rate of the reactant/adsorbatechemical gas to the flow rate of the inert carrier gas can be in a rangefrom about 0.90:0.10 to about 0.05:0.95. A pressure of the example CVDprocess with a remote plasma can be in a range from about 0.1 Torr toabout 40 Torr. The remote plasma of the CVD process may be a CCP. Theplasma generator of the CVD process with a remote plasma can be operatedwith a power in a range from about 10 W to about 1,000 W and with afrequency in a range from about 13.56 MHz to about 40 MHz. The substrateholder of the CVD process may be unbiased. A temperature of the exampleCVD process with a remote plasma can be in a range from 20° C. (e.g.,room temperature) to 400° C., and more particularly, from about 50° C.to about 300° C. A duration of the example CVD process with a remoteplasma can be in a range from about 5 seconds to about 300 seconds.

Since the reactant/adsorbate chemical reacts with the dielectricsurfaces (e.g., as opposed to reacting with another reactant/adsorbatechemical supplied to the process), the formation of the modifiedsurfaces 120 can be reaction limited based on the reaction sitesavailable on the dielectric surfaces. Hence, the modified surfaces 120can be or include hydrophobic functional groups terminating thedielectric surfaces and/or a monolayer of the hydrophobic functionalgroups (e.g., a self-aligned monolayer (SAM)). For example, where thedielectric surfaces include or are Si—OH, the Si—OH of the dielectricsurfaces can react with the reactant/adsorbate chemical, which isR—Si—(CH₃)₃ in this example, to form a modified surface that is orincludes Si—O—Si—(CH₃)₃, where the H from the Si—OH and R functionalgroup from the R—Si—(CH₃)₃ are byproducts from the reaction that areremoved from the surface, such as by purging gas in a dry process and/orrinsing in a wet process. In this example, the —CH₃ groups cause themodified surfaces 120 to be hydrophobic.

The bonding energy between the species Si—(CH₃)₃ in this example and themetallic surfaces of the gate electrodes 116 and one or more optionalconformal layers 114 is larger than the bonding energy between thespecies Si—(CH₃)₃ and oxygen-containing dielectric surfaces. Hence, thespecies Si—(CH₃)₃ bonds to the dielectric surfaces to form the modifiedsurfaces 120 while not significantly bonding with the metallic surfaces.

In some examples, a thermal treatment may be performed, which can removethe reactant/adsorbate chemical that was adsorbed on the metallicsurfaces. For example, the thermal treatment can cause thereactant/adsorbate chemical to be desorbed and/or to evaporate from themetallic surfaces. In some examples, the thermal treatment includes afurnace process, rapid thermal anneal (RTA), or the like. A thermaltreatment may be performed in an active gas, such as hydrogen (H₂),ammonia (NH₃), or the like, at a temperature in a range from about 50°C. to about 400° C., such as about 200° C., for a duration in a rangefrom about 30 seconds to 1 minute. Other thermal treatments may beimplemented.

FIGS. 12A and 12B illustrate the formation of capping layers 122 (e.g.,a metal cap) on metallic surfaces, such as surfaces of the one or moreoptional conformal layers 114 and gate electrodes 116. The cappinglayers 122 can be formed using a selective deposition process thatdeposits the capping layers 122 on the metallic surfaces but does notsignificantly deposit on dielectric surfaces.

In some examples, the selective deposition is a fluorine-free tungstendeposition, and hence, the capping layers 122 can be free of fluorine.In some examples, the selective deposition process, which further is afluorine-free tungsten deposition, is an ALD process that uses ahydrogen (H₂) precursor and a tungsten chloride precursor. The tungstenchloride precursor can be tungsten (V) chloride (WCl₅), tungsten (VI)chloride (WCl₆), another tungsten chloride, or a combination thereof. Insome examples, a cycle of the ALD process can include sequentiallyflowing the tungsten chloride precursor, purging the tungsten chlorideprecursor, flowing the hydrogen precursor, and purging the hydrogenprecursor. In some examples, a cycle of the ALD process can includesequentially flowing the hydrogen precursor, purging the hydrogenprecursor, flowing the tungsten chloride precursor, and purging thetungsten chloride precursor. The ALD process can include performing thecycle any number of times, such as in a range from about 150 cycles toabout 320 cycles. Flowing the tungsten chloride can also include flowinga carrier gas, such as argon, nitrogen, helium, or the like. A ratio ofthe flow rate of the tungsten chloride to the flow rate of the carriergas can be in a range from about 0.90:0.10 to about 0.05:0.95. A flowrate of the mixture of the tungsten chloride precursor and the carriergas can be in a range from about 10 sccm to about 1,000 sccm, such asabout 500 sccm. A flow rate of the tungsten chloride precursor can be ina range from about 10 sccm to about 1,000 sccm, and a flow rate of thecarrier gas can be in a range from about 10 sccm to about 3,000 sccm. Aflow rate of the hydrogen precursor can be in a range from about 100sccm to about 10,000 sccm, such as about 7,000 sccm. A pressure of theALD process can be in a range from about 0.1 Torr to about 40 Torr, suchas about 20 Torr. A temperature of the ALD process can be in a rangefrom about 75° C. to about 500° C., such as about 450° C.

It is believed that the high electron mobility of metallic surfaces(e.g., TiN, TaN, AlTiC, AlTiO, AlTiN, W, etc.) permits the tungstenchloride to react more easily with the metallic surfaces than dielectricsurfaces, which have a lower electron mobility. In the above-describedALD process, it is believed that tungsten chloride reacts with themetallic surface to form a bond between a material of the metallicsurface and tungsten chloride (WCl_(x)) and to form a bond between amaterial of the metallic surface and chlorine that is released from thetungsten chloride precursor. When the hydrogen precursor is flowed, itis believed that the hydrogen reacts with chlorine bonded with themetallic surface and/or chlorine of the tungsten chloride (WCl_(x))bonded with the metallic surface to form hydrochloric acid (HCl), whichis formed as a gaseous byproduct and purged in the flowing and purgingof the hydrogen precursor. Tungsten can therefore be formed on themetallic surfaces. The formed tungsten may include residual chlorine,such as less than about 1%.

In other examples, other processes may be implemented to form thecapping layers 122. For example, any process that permits the selectivedeposition of a metal on a metallic surface can be implemented, such asa CVD, ALD, or another deposition technique that can selectivelydeposit, for example, cobalt, manganese, tungsten, or another metal ormetallic material. An example is selective deposition of cobalt by a CVDprocess. The CVD process can use a cobalt carbonyl precursor mixed withan inert carrier gas. A ratio of the flow rate of the cobalt carbonyl tothe flow rate of the carrier gas can be in a range from about 0.90:0.10to about 0.05:0.95. A flow rate of the mixture of the cobalt carbonyland the carrier gas can be in a range from about 10 sccm to about 1,000sccm. A flow rate of the cobalt carbonyl precursor can be in a rangefrom about 10 sccm to about 1,000 sccm, and a flow rate of the carriergas can be in a range from about 10 sccm to about 3,000 sccm. A pressureof the CVD process can be in a range from about 0.1 Torr to about 40Torr, such as about 20 Torr. A temperature of the CVD process can be ina range from about 20° C. to about 400° C.

In examples implementing the modified surfaces 120, with the modifiedsurfaces 120 present during the deposition of the capping layers 122,precursors, byproducts, etc. of the deposition process for forming thecapping layers 122 can be repelled by the electrostatic force of thehydrophobic modified surfaces 120, which can improve the selectivity ofthe deposition process and reduce damage to dielectric layers, such as alow-k dielectric of the first ILD 100. The improved selectivity andreduced damage can reduce defects and reduce parasitic leakage caused bydamage to the dielectric layers.

As illustrated in FIG. 12A, the capping layers 122 are formed onmetallic surfaces of the replacement gate structure (e.g., top surfacesor the one or more optional conformal layers 114 (e.g., TiN, TaN, AlTiC,AlTiO, AlTiN, etc.), and gate electrodes 116 (e.g., W, etc.)) that areformed by the planarization process (e.g., CMP) described with respectto FIGS. 10A and 10B. The planarization process of FIGS. 10A and 10Bformed top surfaces of the first ILD 100, CESL 96, and gate spacers 86(which surfaces may be modified to be the modified surfaces 120) to becoplanar with the top surfaces of the gate dielectric layers 112 (whichmay also be modified to the modified surfaces 120), one or more optionalconformal layers 114, and gate electrodes 116. Hence, the capping layers122 may have respective top surfaces at a level above the top surfacesof the first ILD 100, CESL 96, gate spacers 86, and gate dielectriclayers 112, which surfaces may be modified to be the modified surfaces120. The capping layers 122 may have a thickness in a range from about30 Å to about 50 Å.

FIGS. 13A and 13B illustrate the formation of a second ILD 130 over themodified surfaces 120 (if implemented, and/or over the first ILD 100,gate spacers 86, CESL 96, and gate dielectric layers 112) and cappinglayers 122. Although not illustrated, in some examples, an etch stoplayer may be deposited over the modified surfaces 120 (if implemented,and/or over the first ILD 100, gate spacers 86, CESL 96, and gatedielectric layers 112) and capping layers 122, and the second ILD 130may be deposited over the ESL. If implemented, the ESL may comprise orbe silicon nitride, silicon carbon nitride, silicon carbon oxide, carbonnitride, the like, or a combination thereof, and may be deposited byCVD, PECVD, ALD, or another deposition technique. The second ILD 130 maycomprise or be silicon dioxide, a low-k dielectric material, such assilicon oxynitride, PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y),Spin-On-Glass, Spin-On-Polymers, silicon carbon material, a compoundthereof, a composite thereof, the like, or a combination thereof. Thesecond ILD 130 may be deposited by spin-on, CVD, FCVD, PECVD, PVD, oranother deposition technique.

FIGS. 14A and 14B illustrate the formation of respective openings 132through the second ILD 130, the first ILD 100 and its modified surface120 (if implemented), and the CESL 96 to the epitaxy source/drainregions 92 to expose at least portions of the epitaxy source/drainregions 92, and through the second ILD 130 to expose at least portionsof the capping layers 122. The second ILD 130, the first ILD 100, andthe CESL 96 may be patterned with the openings 132, for example, usingphotolithography and one or more etch processes.

FIGS. 15A and 15B illustrate the formation of respective conductivefeatures in the openings 132 to the epitaxy source/drain regions 92 andto the capping layers 122. Each conductive feature includes, in theillustrated example, an adhesion layer 140, a barrier layer 142 on theadhesion layer 140, and conductive fill material 146 on the barrierlayer 142, for example. In some examples, each conductive feature to theepitaxy source/drain regions 92 may further include a silicide region144 on the epitaxy source/drain region 92, as illustrated.

The adhesion layer 140 can be conformally deposited in the openings 132(e.g., on sidewalls of the openings 132, exposed surfaces of the epitaxysource/drain regions 92, and exposed surfaces of the capping layers 122)and over the second ILD 130. The adhesion layer 140 may be or comprisetitanium, tantalum, the like, or a combination thereof, and may bedeposited by ALD, CVD, PVD, or another deposition technique. The barrierlayer 142 can be conformally deposited on the adhesion layer 140, suchas in the openings 132 and over the second ILD 130. The barrier layer142 may be or comprise titanium nitride, titanium oxide, tantalumnitride, tantalum oxide, the like, or a combination thereof, and may bedeposited by ALD, CVD, or another deposition technique. In someexamples, at least a portion of the adhesion layer 140 can be treated toform the barrier layer 142. For example, a nitridation process, such asincluding a nitrogen plasma process, can be performed on the adhesionlayer 140 to convert the at least the portion of the adhesion layer 140into the barrier layer 142. In some examples, the adhesion layer 140 canbe completely converted such that no adhesion layer 140 remains and thebarrier layer 142 is an adhesion/barrier layer, while in other examples,a portion of the adhesion layer 140 remains unconverted such that theportion of the adhesion layer 140 remains with the barrier layer 142 onthe adhesion layer 140.

Silicide regions 144 may be formed on the epitaxy source/drain regions92 by reacting upper portions of the epitaxy source/drain regions 92with the adhesion layer 140, and possibly, the barrier layer 142. Ananneal can be performed to facilitate the reaction of the epitaxysource/drain regions 92 with the adhesion layer 140 and/or barrier layer142.

The conductive fill material 146 can be deposited on the barrier layer142 and fill the openings 132. The conductive fill material 146 may beor comprise tungsten, cobalt, copper, ruthenium, aluminum, gold, silver,alloys thereof, the like, or a combination thereof, and may be depositedby CVD, ALD, PVD, or another deposition technique. After the conductivefill material 146 is deposited, excess conductive fill material 146,barrier layer 142, and adhesion layer 140 may be removed by using aplanarization process, such as a CMP, for example. The planarizationprocess may remove excess conductive fill material 146, barrier layer142, and adhesion layer 140 from above a top surface of the second ILD130. Hence, top surfaces of the conductive features and the second ILD130 may be coplanar. The conductive features may be or may be referredto as contacts, plugs, etc.

Although FIGS. 15A and 15B illustrate the conductive features to theepitaxy source/drain regions 92 and the conductive features to thecapping layers 122 being formed simultaneously, the respectiveconductive features may be formed separately and sequentially. Forexample, the openings 132 to the epitaxy source/drain regions 92 may befirst formed, as in FIGS. 14A and 14B, and filled to form conductivefeatures to the epitaxy source/drain regions 92, as in FIGS. 15A and15B. Then, the openings 132 to the capping layers 122 may be formed, asin FIGS. 14A and 14B, and filled to form conductive features to thecapping layers 122, as in FIGS. 15A and 15B. Another order of processingmay be implemented.

FIGS. 16A-B through 19A-B are cross-sectional views of respectiveintermediate structures at intermediate stages in another exampleprocess of forming a semiconductor device in accordance with someembodiments. In this example process, processing proceeds as describedwith respect to FIGS. 2A-B through 10A-B and resumes at FIGS. 16A-B.

FIGS. 16A and 16B illustrate the recessing of metallic components of thereplacement gate structures, such as the one or more optional conformallayers 114 and the gate electrodes 116. The recessing forms recesses 118where the metallic components were recessed. The recessing can beperformed by any suitable etch process and/or cleaning process, such asa process that removes material of the metallic components of thereplacement gate structure at a greater rate than, e.g., the first ILD100, CESL 96, gate spacers 86, and gate dielectric layers 112. Theremoval process can be a dry (e.g., plasma) process and/or a wetprocess. A depth of the recesses 118 can be in a range from about 30 Åto about 50 Å.

In some examples, the removal process is a plasma process that uses anoxygen (O₂) plasma. The plasma process can be an RIE, ICP, CCP, or thelike. Other gases, such as hydrogen (H₂), ammonia (NH₃), or the like,may be used instead of or in addition to the oxygen in the plasmaprocess. A flow rate of the oxygen gas can be in a range from about 5sccm to about 500 sccm. A temperature of the plasma process may be in arange from about 20° C. to about 400° C., such as about 200° C. Apressure of the plasma process may be in a range from about 5 mTorr toabout 10 Torr, such as about 1.1 Torr. A power of the plasma generatorof the plasma process may be in a range from about 100 W to about 40 kW.The substrate holder of the plasma process may be unbiased. A durationof the exposure of the intermediate structure to the plasma of theplasma process can be in a range from about 2 seconds to about 600seconds.

In some examples, the removal process is a wet process. For example, thewet process can be a standard clean (SC) 1 and/or a SC-2. A temperatureof the wet process may be in a range from about 20° C. to about 80° C. Aduration of the wet process can be in a range from about 5 seconds toabout 600 seconds. Other wet processes, such as using different etchantscan be implemented.

FIGS. 17A and 17B illustrate the modification of exposed dielectricsurfaces to have modified surfaces 120. The modification may beperformed as described above with respect to FIGS. 11A and 11B, andhence, further description here is omitted for brevity. As in FIGS. 11Aand 11B, the modification of exposed dielectric surfaces can be omittedin some examples.

The recess 118 causes upper portions of sidewalls of the gate dielectriclayer 112 to be exposed to the modification process, and hence, theupper portions of sidewalls of the gate dielectric layer 112 can havemodified surfaces 120, as illustrated.

FIGS. 18A and 18B illustrate the formation of capping layers 122 (e.g.,a metal cap) on metallic surfaces, such as surfaces of the one or moreoptional conformal layers 114 and gate electrodes 116 where thereplacement gate structures were recessed to form the recesses 118. Theformation of the capping layers 122 may be performed as described abovewith respect to FIGS. 12A and 12B, and hence, further description hereis omitted for brevity. In this example, bottom surfaces of the cappinglayers 122 are below the modified surfaces 120 and/or top surfaces ofthe first ILD 100, CESL 96, gate spacers 86, and gate dielectric layer112, and top surfaces of the capping layers 122 can be above, levelwith, or below the modified surfaces 120 and/or top surfaces of thefirst ILD 100, CESL 96, gate spacers 86, and gate dielectric layer 112.Further, sidewalls of the capping layers 122 can abut the modifiedsurfaces 120 of the upper portions of the sidewalls of the gatedielectric layer 112, as illustrated, and/or can abut the sidewalls ofthe gate dielectric layer 112.

FIGS. 19A and 19B illustrate the formation of a second ILD 130 over themodified surfaces 120 (if implemented, and/or over the first ILD 100,gate spacers 86, CESL 96, and gate dielectric layers 112) and cappinglayers 122. The formation of the second ILD 130 may be performed asdescribed above with respect to FIGS. 13A and 13B, and hence, furtherdescription here is omitted for brevity. Processing may then continue asdescribed above with respect to FIGS. 14A-B through 15A-B.

FIG. 20 is a flow chart of an example process of forming a semiconductordevice in accordance with some embodiments. In operation 202, areplacement gate structure is formed over an active area and in one ormore dielectric structures. An example of operation 202 is describedwith respect to and illustrated in FIGS. 10A and 10B. For example, thereplacement gate structure comprising a gate dielectric layer 112, oneor more optional conformal layers 114, and gate electrode 116 is formedover the fin 74 and in the gate spacers 86, CESL 96, and first ILD 100.

In operation 204, optionally, metallic components of the replacementgate structure are recessed below top surfaces of the one or moredielectric structures. An example of operation 204 is described withrespect to and illustrated in FIGS. 16A and 16B. For example, the one ormore optional conformal layers 114 and gate electrode 116 are recessedbelow top surfaces of the gate spacers 86, CESL 96, first ILD 100, andgate dielectric layer 112.

In operation 206, optionally, exposed dielectric surfaces are modified.Examples of operation 206 are described with respect to and illustratedin FIGS. 11A and 11B and FIGS. 17A and 17B. For example, the topsurfaces of the gate spacers 86, CESL 96, first ILD 100, and gatedielectric layer 112 are modified, and if operation 204 is performed,upper portions of sidewalls of the gate dielectric layer 112 can also bemodified.

In operation 208, a capping layer is formed on the metallic componentsof the replacement gate structure using a selective deposition process.Examples of operation 208 are described with respect to and illustratedin FIGS. 12A and 12B and FIGS. 18A and 18B. For example, a capping layer122 is formed on the one or more optional conformal layers 114 and gateelectrode 116 of the replacement gate structure.

In operation 210, one or more dielectric layers are formed over thecapping layer and over the modified surfaces and/or the one or moredielectric structures. Examples of operation 210 are described withrespect to and illustrated in FIGS. 13A and 13B and FIGS. 19A and 19B.For example, a second ILD 130 is formed over the capping layers 122and/or the first ILD 100, CESL 96, and gate spacers 86.

In operation 212, a conductive feature is formed through the one or moredielectric layers to the capping layer. An example of operation 212 isdescribed with respect to FIGS. 15A and 15B. For example, a conductivefeature including an adhesion layer, a barrier layer, and a conductivefill material is formed through the second ILD 130 to the capping layer122.

FIGS. 21 through 28 are cross-sectional views of respective intermediatestructures at intermediate stages in another example process of forminga semiconductor device in accordance with some embodiments. Thecross-sectional views of FIGS. 21 through 28 correspond with a portionof cross-section A-A of FIG. 1, for example.

FIG. 21 illustrates a portion of the cross-sectional view of FIG. 15A. Aconductive feature is through the second ILD 130, first ILD 100, andCESL 96 to an epitaxy source/drain region 92. The conductive featurecomprises an adhesion layer 140, a barrier layer 142, and a conductivefill material 146. The top surfaces of the adhesion layer 140, barrierlayer 142, and conductive fill material 146 are coplanar with the topsurface of the second ILD 130.

FIG. 22 illustrates the modification of the exposed dielectric surfaceof the second ILD 130 to have a modified surface 150. The modificationmay be performed as described above with respect to FIGS. 11A and 11B,and hence, further description here is omitted for brevity. Hence, thetop surface of the second ILD 130 may be modified to be the modifiedsurface 150.

FIG. 23 illustrates the formation of a capping layer 152 on metallicsurfaces of the conductive feature, such as surfaces of the conductivefill material 146, barrier layer 142, and adhesion layer 140. Theformation of the capping layer 152 may be performed as described abovewith respect to FIGS. 12A and 12B, and hence, further description hereis omitted for brevity.

As illustrated in FIG. 23, the capping layer 152 is formed on metallicsurfaces of the conductive feature that are formed by the planarizationprocess (e.g., CMP) described with respect to FIGS. 15A and 15B. Theplanarization process of FIGS. 15A and 15B formed the top surface of thesecond ILD 130 (which surface may be modified to be the modified surface150) to be coplanar with the top surfaces of the conductive featurecomprising the conductive fill material 146, barrier layer 142, andadhesion layer 140. Hence, the capping layer 152 may have a top surfaceat a level above the top surface of the second ILD 130, which surfacemay be modified to be the modified surface 150. The capping layer 152may have a thickness in a range from about 30 Å to about 50 Å.

FIG. 24 illustrates the formation of a dielectric layer 154 over themodified surface 150 and capping layer 152 with a conductive feature 156through the dielectric layer 154 contacting the capping layer 152. Thedielectric layer 154 may be or include an ESL and/or anintermetallization dielectric (IMD). An ESL can be deposited on themodified surface 150 and the capping layer 152. The ESL may comprise orbe silicon nitride, silicon carbon nitride, silicon carbon oxide, carbonnitride, the like, or a combination thereof, and may be deposited byCVD, PECVD, ALD, or another deposition technique. The IMD, which may bedeposited over the ESL if the ESL is implemented, may comprise or besilicon dioxide, a low-k dielectric material, such as siliconoxynitride, PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y), Spin-On-Glass,Spin-On-Polymers, silicon carbon material, a compound thereof, acomposite thereof, the like, or a combination thereof. The IMD may bedeposited by spin-on, CVD, FCVD, PECVD, PVD, or another depositiontechnique.

The conductive feature 156 contacting the capping layer 152 may be orinclude, for example, a via or another conductive feature. Theconductive feature 156 may be formed using a damascene process, such asa dual damascene process. An opening may be formed through thedielectric layer 154 using photolithography and one or more etchprocesses. The conductive feature 156 can be formed in the opening, forexample, by depositing one or more materials of the conductive feature156 in the opening. For example, the conductive feature 156 can includea barrier layer formed conformally in the opening and a conductive fillmaterial formed on the barrier layer. The barrier layer may be orcomprise titanium nitride, titanium oxide, tantalum nitride, tantalumoxide, the like, or a combination thereof, and may be deposited by ALD,CVD, or another deposition technique. The conductive fill material canbe deposited on the barrier layer and fill the opening. The conductivefill material may be or comprise copper, tungsten, cobalt, ruthenium,aluminum, gold, silver, alloys thereof, the like, or a combinationthereof, and may be deposited by CVD, ALD, PVD, plating, or anotherdeposition technique. After the conductive fill material is deposited,excess conductive fill material and barrier layer may be removed byusing a planarization process, such as a CMP, for example.

FIG. 25 illustrates the formation of an IMD 170 with a conductivefeature over the intermediate structure of FIG. 24. The IMD 170 may beat any IMD level. For example, the IMD 170 may be the immediately nextIMD over the intermediate structure of FIG. 24 (e.g., as a part of orimmediately over the dielectric layer 154) or any number of IMD levelsmay be between the dielectric layer 154 and the IMD 170. The IMD 170 maycomprise or be silicon dioxide, a low-k dielectric material, such assilicon oxynitride, PSG, BSG, BPSG, USG, FSG, OSG, SiO_(x)C_(y),Spin-On-Glass, Spin-On-Polymers, silicon carbon material, a compoundthereof, a composite thereof, the like, or a combination thereof. TheIMD 170 may be deposited by spin-on, CVD, FCVD, PECVD, PVD, or anotherdeposition technique.

The conductive feature includes a barrier layer 172 and conductive fillmaterial 174. The conductive feature may be formed using a damasceneprocess, such as a dual damascene process. The conductive feature may bea conductive line, pad, or the like, and may further comprise a via toan underlying conductive feature. An opening and/or recess may be formedin and/or through the IMD 170 using photolithography and one or moreetch processes. The barrier layer 172 is formed conformally in theopening and/or recess, and the conductive fill material 174 is formed onthe barrier layer 172. The barrier layer 172 may be or comprise titaniumnitride, titanium oxide, tantalum nitride, tantalum oxide, the like, ora combination thereof, and may be deposited by ALD, CVD, or anotherdeposition technique. The conductive fill material 174 can be depositedon the barrier layer 172 and fill the opening and/or recess. Theconductive fill material 174 may be or comprise copper, tungsten,cobalt, ruthenium, aluminum, gold, silver, alloys thereof, the like, ora combination thereof, and may be deposited by CVD, ALD, PVD, plating,or another deposition technique. After the conductive fill material 174is deposited, excess conductive fill material 174 and barrier layer 172may be removed by using a planarization process, such as a CMP, forexample.

FIG. 26 illustrates the modification of the exposed dielectric surfaceof the IMD 170 to have a modified surface 180. The modification may beperformed as described above with respect to FIGS. 11A and 11B, andhence, further description here is omitted for brevity. Hence, the topsurface of the IMD 170 may be modified to be the modified surface 180.

FIG. 27 illustrates the formation of a capping layer 182 on metallicsurfaces of the conductive feature, such as surfaces of the conductivefill material 174 and barrier layer 172. The formation of the cappinglayer 182 may be performed as described above with respect to FIGS. 12Aand 12B, and hence, further description here is omitted for brevity.

As illustrated in FIG. 27, the capping layer 182 is formed on metallicsurfaces of the conductive feature that are formed by the planarizationprocess (e.g., CMP) described with respect to FIG. 25. The planarizationprocess of FIG. 25 formed the top surface of the IMD 170 (which surfacemay be modified to be the modified surface 180) to be coplanar with thetop surfaces of the conductive feature comprising the conductive fillmaterial 174 and barrier layer 172. Hence, the capping layer 182 mayhave a top surface at a level above the top surface of the IMD 170,which surface may be modified to be the modified surface 180. Thecapping layer 182 may have a thickness in a range from about 30 Å toabout 50 Å.

FIG. 28 illustrates the formation of a dielectric layer 184 over themodified surface 180 and capping layer 182 with a conductive feature 186through the dielectric layer 184 contacting the capping layer 182. Thedielectric layer 184 may be or include an ESL and/or an IMD. An ESLand/or IMD and the conductive feature 186 may be formed as describedabove with respect to FIG. 24, and hence, further description here isomitted for brevity.

Although not illustrated, the conductive features of FIGS. 21 and 25 canbe recessed before the respective dielectric surfaces are modified inFIGS. 22 and 26. The recessing may be performed as described above withrespect to FIGS. 16A and 16B, and hence, further description here isomitted for brevity.

Recessing can permit upper portions of sidewalls of the second ILD 130to be modified (e.g., in the processing of FIG. 22) where the conductivefeature was recessed. When the conductive feature of FIG. 21 isrecessed, the capping layer 152 has a bottom surface that is below themodified surface 150 and/or top surface of the second ILD 130, and a topsurface of the capping layer 152 can be above, level with, or below themodified surface 150 and/or top surfaces of the second ILD 130. Further,sidewalls of the capping layer 152 can abut the modified surfaces 150 ofthe upper portions of the sidewalls of the second ILD 130 and/or canabut the sidewalls of the second ILD 130. Similarly, recessing canpermit upper portions of sidewalls of the IMD 170 to be modified (e.g.,in the processing of FIG. 26) where the conductive feature was recessed.When the conductive feature (comprising conductive fill material 174) ofFIG. 25 is recessed, the capping layer 182 has a bottom surface that isbelow the modified surface 180 and/or top surface of the IMD 170, and atop surface of the capping layer 182 can be above, level with, or belowthe modified surface 180 and/or top surfaces of the IMD 170. Further,sidewalls of the capping layer 182 can abut the modified surfaces 180 ofthe upper portions of the sidewalls of the IMD 170 and/or can abut thesidewalls of the IMD 170.

FIG. 29 is a flow chart of an example process of forming a semiconductordevice in accordance with some embodiments. In operation 252, a firstconductive feature is formed in a first dielectric layer. Examples ofoperation 252 are described with respect to and illustrated in FIG. 21and FIG. 25. For example, the conductive feature comprising the adhesionlayer 140, barrier layer 142, and conductive fill material 146 is formedin the second ILD 130, first ILD 100, and CESL 96. As another example,the conductive feature comprising the barrier layer 172 and conductivefill material 174 is formed in the IMD 170.

In operation 254, optionally, the first conductive feature is recessedbelow a top surface of the first dielectric layer. Examples of operation254 are described above. For example, the conductive feature (comprisingthe conductive fill material 146) of FIG. 21 can be recessed below thetop surface of the second ILD 130. As another example, the conductivefeature (comprising the conductive fill material 174) of FIG. 25 can berecessed below the top surface of the IMD 170.

In operation 256, exposed dielectric surfaces, e.g., of the firstdielectric layer, are modified. Examples of operation 256 are describedwith respect to and illustrated in FIG. 22 and FIG. 26. As examples, thetop surfaces of the second ILD 130 and IMD 170 are modified.

In operation 258, a capping layer is formed on the first conductivefeature using a selective deposition process. Examples of operation 258are described with respect to and illustrated in FIG. 23 and FIG. 27. Asexamples, capping layer 152 and 182 are formed on conductive featurescomprising, respectively, (i) the conductive fill material 146, barrierlayer 142, and adhesion layer 140, and (ii) the conductive fill material174 and barrier layer 172.

In operation 260, a second dielectric layer is formed over the cappinglayer and over the modified dielectric surface. Examples of operation260 are described with respect to and illustrated in FIG. 24 and FIG.28. For example, the dielectric layers 154 and 184 are formed over thecapping layers 152 and 182 and the modified surfaces 150 and 180,respectively.

In operation 262, a second conductive feature is formed through thesecond dielectric layer to the capping layer. Examples of operation 262are described with respect to and illustrated in FIG. 24 and FIG. 28.For example, conductive features 156 and 186 are formed through thedielectric layers 154 and 184 to the capping layers 152 and 182,respectively.

Some embodiments may achieve advantages. For example, a surfacemodification process to modify a dielectric surface of a dielectriclayer can create a selective protection layer on the dielectric layer.The protection layer (e.g., modified dielectric surface) can increaseselectivity of a subsequent selective deposition process, such as forselectively depositing a capping layer (e.g., metal cap), and can reducedamage of the dielectric layer. For example, the protection layer (e.g.,modified dielectric surface) can terminate dangling bonds on the surfaceof the dielectric layer, which can reduce unexpected deposition of metalduring the selective deposition of the capping layer. Further, theprotection layer can reduce process gases and metal ions from attackingand diffusing into the dielectric layer. Hence, defects in and leakagethrough the dielectric layer can be reduced.

In some examples, forming a capping layer on a gate structure, such as areplacement gate structure, can reduce gate resistance (R_(g)),particularly in short channel devices. In some instances, such as in areplacement gate process where a dimension of the gate structure (e.g.,in the channel length direction) is small, high resistance conductivecomponents, such as barrier, capping, and/or work-function tuninglayers, can increase in size proportionally relative to the dimension ofthe gate structure, whereas a low resistance conductive component, suchas the gate electrode, decreases in size proportionally relative to thedimension of the gate structure. A capping layer formed on thereplacement gate structure can offset some increase in resistance as aresult of the decreasing in the size of the dimension of the replacementgate structure. Further, example processes described herein can avoidmasking and patterning processes, and thereby avoid processes that couldincrease cost, while reducing the gate resistance. Advantages of someembodiments, such as the capping layer on a gate structure and/or thesurface modification process, can be particularly applicable in smalltechnology nodes, such as 7 nm and smaller.

An embodiment is a method. A conductive feature is formed in a firstdielectric layer. The conductive feature has a metallic surface, and thefirst dielectric layer has a dielectric surface. The dielectric surfaceis modified to be hydrophobic by performing a surface modificationtreatment. After modifying the dielectric surface, a capping layer isformed on the metallic surface by performing a selective depositionprocess. A second dielectric layer is formed over the capping layer andthe dielectric surface.

Another embodiment is a structure. The structure includes a firstdielectric layer over a substrate, a conductive feature in the firstdielectric layer, and a metal cap on the conductive feature. The firstdielectric layer has a dielectric surface terminated with a speciesincluding a hydrophobic functional group. The structure also includes asecond dielectric layer on the dielectric surface and the metal cap.

A further embodiment is a method. A gate structure is formed over anactive area on a substrate. A surface of the gate structure is exposedthrough a first dielectric layer. A capping layer is formed on thesurface of the gate structure by performing a selective depositionprocess. A second dielectric layer is formed over the capping layer andthe first dielectric layer. A conductive feature is formed through thesecond dielectric layer to the capping layer.

A yet further embodiment is a structure. The structure includes a gatestructure over an active area on a substrate, a first dielectric layerover the substrate and along the gate structure, a metal cap on the gatestructure, a second dielectric layer over the metal cap and the firstdielectric layer, and a conductive feature through the second dielectriclayer to the metal cap.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A structure comprising: a first dielectric layerover a substrate, the first dielectric layer having a dielectric surfaceterminated with a species comprising a hydrophobic functional group,wherein the hydrophobic functional group is in a monolayer ofhydrophobic functional groups along a top surface of the firstdielectric layer; a conductive feature in the first dielectric layer; ametal cap on the conductive feature, wherein the metal cap comprises afluorine free tungsten; and a second dielectric layer on the dielectricsurface and the metal cap.
 2. The structure of claim 1, wherein asurface of the conductive feature, on which the metal cap is disposed,is level with the dielectric surface.
 3. The structure of claim 1,wherein the hydrophobic functional group is a hydrocarbon.
 4. Thestructure of claim 1, wherein the hydrophobic functional group has ageneral form of —C_(X)H_(2X+1).
 5. The structure of claim 1, wherein themetal cap has a thickness of between about 30 Å to about 50 Å.
 6. Thestructure of claim 1, wherein the metal cap comprises tungsten.
 7. Thestructure of claim 1, wherein the conductive feature is recessed from asurface of the first dielectric layer.
 8. The structure of claim 1,wherein the metal cap comprises cobalt.
 9. A structure comprising: agate structure over an active area on a substrate; a first dielectriclayer over the substrate and along the gate structure; a monolayer ofhydrophobic functional groups along a top surface of the firstdielectric layer; a metal cap on the gate structure, wherein the metalcap has a concentration of chlorine that is less than 1%; a seconddielectric layer over the metal cap and the first dielectric layer; anda conductive feature through the second dielectric layer to the metalcap.
 10. The structure of claim 9, wherein the metal cap comprisestungsten.
 11. The structure of claim 9, wherein the metal cap has athickness in a range from 30 Å to 50 Å.
 12. The structure of claim 9,wherein a bottom surface of the metal cap is level with a top surface ofthe first dielectric layer.
 13. The structure of claim 9, wherein thegate structure comprises: a gate dielectric layer having a firsthorizontal portion, a first vertical portion, and a second verticalportion; a work-function tuning layer having a second horizontalportion, a third vertical portion, and a fourth vertical portion, thesecond horizontal portion of the work-function tuning layer being overthe first horizontal portion of the gate dielectric layer, the thirdvertical portion and the fourth vertical portion of the work-functiontuning layer being disposed laterally between the first vertical portionand the second vertical portion of the gate dielectric layer; and a gateelectrode disposed laterally between the third vertical portion and thefourth vertical portion of the work-function tuning layer, wherein themetal cap is on top surfaces of the gate electrode and the thirdvertical portion and the fourth vertical portion of the work-functiontuning layer.
 14. The structure of claim 9, wherein at least one of thehydrophobic functional groups has a general form of —C_(X)H_(2X+1). 15.The structure of claim 9, wherein the metal cap extends away from thesubstrate further than the monolayer of the hydrophobic functionalgroups.
 16. A structure comprising: a semiconductor fin; a gatestructure over the semiconductor fin; spacers adjacent to the gatestructure; an interlayer dielectric adjacent to the spacers, wherein theinterlayer dielectric is planar with the spacers at a first surface; amonolayer of a hydrophobic functional group extending along the firstsurface from over the interlayer dielectric to over the spacers; and acapping layer in physical contact with the gate structure, the cappinglayer being in physical contact with a sidewall of the monolayer of thehydrophobic functional group, wherein the capping layer comprises afluorine free tungsten.
 17. The structure of claim 16, wherein thehydrophobic functional group has a general form of —C_(X)H_(2X+1). 18.The structure of claim 16, wherein the capping layer has a thickness ofbetween about 30 Å to about 50 Å.
 19. The structure of claim 16, whereinthe capping layer has a concentration of chlorine that is less than 1%.20. The structure of claim 16, wherein the capping layer comprisescobalt.